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SSS 2011-01-24

时间:2011-02-11 06:45来源:互联网 提供网友:qi2261   字体: [ ]
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    (单词翻译:双击或拖选)

This is Scientific American's 60-Second Science. I'm John Matson. Got a minute?

In a laboratory vault1 outside Paris is a small cylinder2 of platinum–iridium alloy3 that serves as the standard for all mass measurements worldwide. By an 1889 international accord, the mass of this metal cylinder defines the kilogram.

But that may soon change. The kilogram is the only unit of measurement still based on a man-made artifact. A second of time, for instance, is now defined in terms of an electron transition of the cesium atom. And the meter is tied to the speed of light. Those standards are universal and unchanging—unlike the official kilogram. The reference cylinder's mass has drifted slightly through the years—not enough to throw off your bathroom scale, but enough to bother measurement scientists.

Some of them are meeting January 24th at the Royal Society in London to discuss future improvements to the measurement units. The plan is to eventually relate the kilogram to a universal number known as Planck's constant. But the technology needed to do that is not yet fully4 developed. So, for the time being, that little metal cylinder will just have to keep pulling its weight. I mean, mass.

Thanks for the minute. For Scientific American's 60-Second Science, I'm John Matson.


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1 vault 3K3zW     
n.拱形圆顶,地窖,地下室
参考例句:
  • The vault of this cathedral is very high.这座天主教堂的拱顶非常高。
  • The old patrician was buried in the family vault.这位老贵族埋在家族的墓地里。
2 cylinder rngza     
n.圆筒,柱(面),汽缸
参考例句:
  • What's the volume of this cylinder?这个圆筒的体积有多少?
  • The cylinder is getting too much gas and not enough air.汽缸里汽油太多而空气不足。
3 alloy fLryq     
n.合金,(金属的)成色
参考例句:
  • The company produces titanium alloy.该公司生产钛合金。
  • Bronze is an alloy of copper and tin.青铜是铜和锡的合金。
4 fully Gfuzd     
adv.完全地,全部地,彻底地;充分地
参考例句:
  • The doctor asked me to breathe in,then to breathe out fully.医生让我先吸气,然后全部呼出。
  • They soon became fully integrated into the local community.他们很快就完全融入了当地人的圈子。
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